From mboxrd@z Thu Jan  1 00:00:00 1970
From: mark.rutland@arm.com (Mark Rutland)
Date: Thu, 12 Dec 2013 10:36:09 +0000
Subject: [PATCH 1/6] arm64: Add asm/cpu.h
In-Reply-To: <52A95CB3.2030805@linaro.org>
References: <1386767606-6391-1-git-send-email-broonie@kernel.org>
 <20131211141018.GC596@darko.cambridge.arm.com>
 <20131211142308.GY11468@sirena.org.uk>
 <20131211142705.GE596@darko.cambridge.arm.com>
 <52A95CB3.2030805@linaro.org>
Message-ID: <20131212103608.GA12106@e106331-lin.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Dec 12, 2013 at 06:50:27AM +0000, Hanjun Guo wrote:
> On 2013-12-11 22:27, Catalin Marinas wrote:
> > On Wed, Dec 11, 2013 at 02:23:08PM +0000, Mark Brown wrote:
> >> On Wed, Dec 11, 2013 at 02:10:19PM +0000, Catalin Marinas wrote:
> >>> On Wed, Dec 11, 2013 at 01:13:21PM +0000, Mark Brown wrote:
> >>
> >>>> +struct cpuinfo_arm {
> >>>> +	struct cpu	cpu;
> >>>> +	u64		cpuid;
> >>>> +#ifdef CONFIG_SMP
> >>>> +	unsigned int	loops_per_jiffy;
> >>>> +#endif
> >>>> +};
> >>
> >>> How is this structure used? I haven't seen the ACPI code doing anything
> >>> with struct cpu (though I haven't dug deep enough). Also loops_per_jiffy
> >>> is useless, that's related to the delay loop based on the generic timer.
> >>
> >> Now I look again we can probably drop this for the toplogy work - it had
> >> been pulled in as part of pulling things in from pre-v8 and the cpuid
> >> was used in the code while I was working on it but isn't any more unless
> >> I'm misreading the code.  
> >>
> >> I don't know what the ACPI guys are doing wtih it, I just saw they added
> >> the same thing.
> > 
> > It looked to me that for ACPI and empty asm/cpu.h file would do for now.
> > There are a couple of prototypes for CPU hotplug I think but haven't
> > seen the structure used (not even the x86_cpu one).
> 
> In ACPI code, only struct cpu is used for ACPI based CPU hotplug, here
> is the code will send to upstream when the ACPI core for ARM is ready.
> 
> ---
>  arch/arm64/include/asm/cpu.h |    5 +++++
>  arch/arm64/kernel/topology.c |   26 ++++++++++++++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/cpu.h b/arch/arm64/include/asm/cpu.h
> index dbeb98d..5613e09 100644
> --- a/arch/arm64/include/asm/cpu.h
> +++ b/arch/arm64/include/asm/cpu.h
> @@ -20,6 +20,11 @@ struct cpuinfo_arm {
>  #endif
>  };
> 
> +#ifdef CONFIG_HOTPLUG_CPU
> +extern int arch_register_cpu(int cpu);
> +extern void arch_unregister_cpu(int cpu);
> +#endif
> +
>  DECLARE_PER_CPU(struct cpuinfo_arm, cpu_data);
> 
>  #endif
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index cb548f1..5c8e69c 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -18,3 +18,29 @@ void arch_fix_phys_package_id(int num, u32 slot)
>  }
>  EXPORT_SYMBOL_GPL(arch_fix_phys_package_id);
> 
> +#ifdef CONFIG_HOTPLUG_CPU
> +int __ref arch_register_cpu(int cpu)
> +{
> +       struct cpuinfo_arm *cpuinfo = &per_cpu(cpu_data, cpu);
> +
> +       /* BSP cann't be taken down on arm */
> +       if (cpu)
> +               cpuinfo->cpu.hotpluggable = 1;

_why_ does the ACPI standard prohibit hotplugging the boot CPU?

In non-ACPI systems we can hotplug out the boot CPU (we can do so under
KVM using PSCI).

I note that the x86 arch_register_cpu allows CPU0 to be hotpluggable on
Intel systems as long as there are no dependencies on CPU0 being
active. Surely we can test for something more fine-grained rather than
disallowing CPU0 hotplug outright?

How does this interact with the existing arm64 hotplug code?

Thanks,
Mark.